Gate driver circuit for switching device

ABSTRACT

A gate driver circuit of a voltage drive type power semiconductor switching device capable of speeding up di/dt and dv/dt even during large-current driving to thereby reduce the switching loss is disclosed. This power semiconductor switching device gate driving circuit includes a drive circuit which applies a drive signal to the gate electrode of the power semiconductor switching device and a measurement unit for measuring a flow current of the power semiconductor switching device. Based on a detected value of the flow current of the power semiconductor switching device, the gate is made variable in mirror voltage thereof.

FIELD OF THE INVENTION

The present invention relates to gate driver circuitry of voltage-drivenpower semiconductor switching devices adaptable for use in electricpower conversion apparatus.

Voltage-driven power semiconductor circuit elements include metal oxidesemiconductor field effect transistors (MOSFETs) and insulated-gatebipolar transistors (IGBTs), which are recently under dramatic advancesin designs for achievement of higher breakdown voltage and largercurrent. One typical prior art MOSFET/IGBT gate driver circuit is shownin FIG. 6. Some typical voltage/current waveforms in the circuit of FIG.6 are shown in FIG. 7, such as the waveforms of a gate voltage, gatecurrent, collector current and collector-emitter current in the case ofan IGBT being driven to perform its switching operations. The case of asmall current is indicated by dotted line, and the case of a largecurrent is by solid line.

Prior known techniques for controlling the collector current waveformand the collector-emitter voltage waveform are disclosed inJP-A-2000-228868, paragraph Nos. 0010 to 0014, and JP-A-2000-232347,paragraph Nos. 0057 to 0072. JP-A-2000-228868 discloses therein atechnique for controlling the rise rate of current (di/dt) and voltagerise rate (dv/dt) when IGBT turns on and off in response to receipt of adetected value of the gate voltage of the IGBT. JP-A-2000-232347 teachesa gate voltage control technique by use of a gate circuit, whichincludes a first on-gate circuit that supplies a first on-gate currentand a second on-gate circuit for supplying a second on-gate currentafter the elapse of a prespecified length of time since the start-up ofsupplying the first on-gate current.

FIG. 7 shows the waveforms of a gate voltage, gate current, collectorcurrent and collector voltage in the case of an IGBT being driven toperform switching. The case of a small current is indicated by dottedline, while the case of a large current is by solid line. When the IGBTturns on, its gate current Ig that flows within a mirror period isalmost determinable by the following equation.Ig=(Vg−Vth)/Rg,where Vg is the control gate voltage, Vth is the threshold voltageequivalent to a mirror voltage, and Rg is the gate resistance. Uponexecution of large-current driving, the mirror voltage Vth becomesgreater in value. Thus, as the collector current increases in magnitude,the mirror-period gate current Ig becomes smaller. When the gate currentIg becomes less, di/dt and dv/dt at the time the IGBT turns on and offbecome moderate—i.e., their profiles are ramped more gently. This posesa drawback as to the lack of an ability to perform switching at highspeeds.

Although the techniques as disclosed in JP-A-2000-228868 andJP-A-2000-232347 involve teachings as to the control of di/dt and dv/dtin IGBT's turn-on/off events, these are not the control scheme pursuantto a current flowing in main circuitry. For this reason, control basedon whether the current is large or small cannot be carried out.Accordingly, the prior art approaches are faced with a problem whichfollows: upon execution of large-current driving, di/dt and dv/dt becomemoderate, resulting in the loss becoming greater.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a technique forincreasing the current rise rate di/dt and voltage rise rate dv/dt evenwhen performing large-current driving to thereby reduce the switchingloss.

To attain the foregoing object, a power semiconductor switching devicegate driving circuit incorporating the principles of this invention isarranged to include a drive circuit for giving a drive signal to thegate electrode of a voltage-driven power semiconductor switching deviceand a measurement unit operative to measure an electrical currentflowing in the power semiconductor switching device. Based on a detectedvalue of the flow current of the power semiconductor switching device,the gate is made variable in mirror voltage thereof. Further, performingdetection of a gate voltage simultaneously makes it possible to achievecontrol with higher accuracy.

In accordance with another aspect of the invention, a powersemiconductor switching device gate driver circuit is provided, whichincludes a drive circuit for applying a drive signal to the gateelectrode of a voltage-driven power semiconductor switching device and ameasurement unit for measuring a flow current of the power semiconductorswitching device. A gate driver circuit of the power semiconductorswitching device includes a constant current circuit. Based on adetected value of the flow current of the power semiconductor switchingdevice, a gate current is varied in magnitude.

As the gate current within a mirror period of the switching device iscontrolled in response to receipt of the detected value of a maincircuit current of the voltage-driven power semiconductor switchingdevice, it is possible to provide enhanced control in a way wellpursuant to a large or small current. This makes it possible to speed updi/dt and dv/dt even upon execution of large-current driving, thereby toenable reduction of the switching loss.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a driver circuit of power semiconductorswitching devices of an embodiment 1.

FIG. 2 is a detailed circuit diagram of the power semiconductor devicedriver circuit of the embodiment 1.

FIG. 3 shows some major switching waveforms of an IGBT in Embodiment 1.

FIG. 4 is a block diagram of a driver circuit of power semiconductordevices of an embodiment 2.

FIG. 5 is a detailed circuit diagram of the power semiconductor devicedriver circuit of Embodiment 2.

FIG. 6 is a circuit diagram of a prior known MOSFET/IGBT gate drivercircuit.

FIG. 7 shows major switching waveforms of an IGBT in the prior artcircuit of FIG. 6.

FIG. 8 is a block diagram of a driver circuit of power semiconductordevices of an embodiment 3.

FIG. 9 is a detailed circuit diagram of the power semiconductor devicedriver circuit of Embodiment 3.

FIG. 10 depicts switching waveforms of an IGBT in Embodiment 3.

FIG. 11 is a block diagram of a driver circuit of power semiconductordevices of Embodiment 4.

FIG. 12 is a block diagram of a driver circuit of power semiconductordevices of Embodiment 5.

FIG. 13 is a block diagram of a driver circuit of power semiconductordevices of Embodiment 6.

DETAILED DESCRIPTION OF THE INVENTION

Several embodiments of this invention will be described in detail withreference to the accompanying drawings below.

Embodiment 1

FIG. 1 shows, in block diagram form, a gate driver circuit for powersemiconductor switching devices in accordance with one embodiment ofthis invention. The driver circuit as shown herein is arranged to have ahalf-bridge IGBT module configuration. On its lower arm side, avoltage-driven switching device such as IGBT 31 and a “free-wheel” diode32 are connected together in parallel. On an upper arm side, an IGBT 33which is a voltage-driven switching device and a freewheel diode 34 areparallel-coupled together. The node between upper and lower arm isconnected to an electrical motor 36. In this embodiment, a currentflowing in this motor is detected and measured by a current transformer16. The IGBT 31 for the lower arm has its gate terminal which isconnected to a lower arm driver circuit 21 incorporating the principlesof this invention, while the IGBT 33 for the upper arm has a gate nodethat is coupled to an upper arm driver circuit 22 of this invention. Inthe illustrative embodiment the current transformer 16 measures amain-circuit current of IGBTs and then inputs its measured value to agate resistance changeover control unit 11. Additionally, it measures anIGBT gate voltage and inputs a resultant measured value to the gateresistance changeover controller 11. An output signal of this gateresistance changeover controller 11 is used to vary a gate resistor 12.

A detailed configuration of the embodiment driver circuit of FIG. 1 isdepicted in FIG. 2, specifically using the arm driver circuit 21 coupledto the IGBT 31 and the diode 32 as an example. In FIG. 2, the same partsor components are designated by the same reference numerals as used inFIG. 1. See FIG. 6, which shows a prior art standard IGBT gate drivercircuit for MOSFETs or IGBTs. In the prior art gate driver circuit, itsfor connection to a drive/protection circuit 51 and the gate terminal ofIGBT is made up of a gate resistor 41, an npn transistor 42 and a pnptransistor 43. By contrast, this embodiment is provided with a gatevoltage determination unit 52 and a main-circuit current determinationunit 53, coupled to the pMOSFET 44 through gate 54 for causing thepMOSFET 44 to turn on in the case where the main-circuit current islarge in magnitude and also while the gate voltage is within a mirrorperiod, thereby lessening the gate resistance. A similar arrangementwith units 52 and 53 is also provided for driving nMOSFET 46 in aninverse manner to pMOSFET 44. Resistors 45 and 47 are respectivelyprovided in parallel with the source drain paths of pMOSFET 44 andnMOSFET 45.

FIG. 7 shows some typical waveforms of a gate voltage, a gate current, acollector current and a collector-emitter voltage in the prior art gatedriver circuit of FIG. 6 in case IGBT performs a switching operation.Those waveforms obtained in the case of a small current are indicated bydotted line; the case of a large current is by solid line. When IGBTturns on, a gate current Ig that flows within the mirror period isalmost determinable by an equation which follows.Ig=(Vg−Vth)/Rg,where Vg is the control gate voltage, Vth is the threshold voltage,i.e., mirror voltage, and Rg is the gate resistance.

Upon execution of large-current driving, the mirror voltage Vth becomesgreater in value; thus, the gate current Ig within the mirror periodbecomes smaller with an increase in collector current. As the gatecurrent Ig becomes less, the rise rate of current di/dt and rise rate ofvoltage dv/dt at IGBT's turn-on/off events become moderate, i.e.,decrease in gradient of profile. Accordingly, the prior art gate drivercircuit suffers from the disadvantage as to the lack of an ability toperform high-speed switching operations.

Turning to FIG. 3, the waveforms of a gate voltage, gate current,collector current and collector-emitter voltage are shown in the casewhere IGBT turns on with the flow of a large current in this embodiment.In FIG. 3, solid lines are used to indicate this embodiment whereasdotted lines are for the prior art. In this embodiment, the gate voltagedecider 52 and main-circuit current decider 53 are provided for causingthe pMOSFET 44 to turn on while the gate voltage is within the mirrorperiod when the main-circuit current is large, thereby to lower the gateresistance. Lowering the gate resistance during large-current drivingmakes it possible to speed up the di/dt and dv/dt.

In this embodiment, the gate current of the mirror period of thevoltage-driven power semiconductor switching device is controlled inconformity to a detection value of the main-circuit current of suchswitching device whereby it is possible to provide control in a waydepending upon whether it is a large current or a small current. Thismakes it possible even during large-current driving to speed up di/dtand dv/dt, thus enabling reduction of the switching loss.

Although the description above is drawn to the operation in the turn-onevent, it is also possible by using similar arrangement in a turn-offevent in this embodiment to speed up di/dt and dv/dt, thereby enablingreduction of the switching loss.

Although this embodiment uses the single unit of main-circuit currentdecider 53, more than two main-circuit current deciders 53 may be usedalong with the pMOSFET 44 and a resistor 45. In this case, multi-levelcontrollability is attainable. Additionally, the scheme for currentdetection is achievable by alternative use of three shunt resistors orone shunt resistor in place of the current transformer 16. While in thisembodiment IGBTs are used as the switching devices thereof, theprincipal concept is also applicable to other types of voltage-drivenpower semiconductor circuit elements such as MOSFETs, and also,obviously, to silicon carbide (SiC) devices other than silicon (Si)ones.

Embodiment 2

A power semiconductor device driver circuit in accordance with anotherembodiment of this invention is shown in FIG. 4 in block diagram form.In FIG. 4, similar parts or components are designated by the samereference numerals as used in FIG. 1 of Embodiment 1. A detailedconfiguration of the driver circuit of FIG. 4 is shown in FIG. 5,wherein like parts are indicated by like reference numerals.

This embodiment is different from Embodiment 1 in that the former lacksfeedback of the gate voltage. Even in the absence of such gate voltagefeedback feature, the mirror period of IGBT is presumable from the delaytime of a pulse width modulation (PWM) signal involved. To this end,this embodiment is provided with a PWM signal delay circuit 55. Owing tothis delay circuit 55, the gate-voltage/gate-current control such asshown in FIG. 3 is realizable. Thus it is possible to speed up di/dt anddv/dt even during large-current driving in a way responding to adetected value of the main-circuit current of the voltage-driven powersemiconductor switching device, thereby enabling appreciable reductionof the switching loss.

Embodiment 3

A power semiconductor device driver circuit in accordance with stillanother embodiment of the invention is shown in FIG. 8 in block diagramform. Like parts or components are denoted by like reference charactersas used in FIG. 1 of Embodiment 1. In a drive circuit 21 for use in thelower arm of this embodiment, a current transformer 16 is provided tomeasure a main-circuit current of IGBT. From a measurement result ofsuch IGBT main-circuit current, a voltage control signal or “command” iscreated by a signal generation unit 13 and is then given to a constantcurrent circuit 14. In this way, the constant current circuit 14 drivesthe IGBT 31.

A detailed configuration of the constant current circuit 14 of the FIG.8 embodiment is shown in FIG. 9, wherein like parts are designated bylike reference numerals. The constant current circuit 14 is generallymade up of operational amplifiers 62-63, resistors 64-65, pMOSFET 66 andnMOSFET 67, and is operatively responsive to receipt of a commandvoltage from the signal generator 13 for performing constant currentcontrol. After completion of the constant current control, the pMOSFET68 and nMOSFET 69 cause the gate voltage of IGBT 31 to be fixed eitherto the power supply voltage of a gate driver circuit control powersupply module 37 or to ground potential.

See FIG. 10, which shows the waveforms of a gate voltage, gate current,collector current and collector voltage in case IGBT turns on inassociation with the flow of a large current in this embodiment. In FIG.10, solid lines are used for indication of this embodiment whereasdotted lines are for the prior art. In this embodiment, upon executionof large-current driving, the signal generator 13 and constant currentcircuit 14 permit the gate current to increase within the mirror periodwhereby the gate drivability is improved so that it is possible to speedup di/dt and dv/dt.

Embodiment 4

A power semiconductor device driver circuit in accordance with a furtherembodiment is shown in FIG. 11 in block diagram form. Like parts aredenoted by like reference characters as used in FIG. 8 of Embodiment 3.In this embodiment, a detected value of the gate voltage is fed back tosignal generator 13. Feedback of the detected value of gate voltagemakes it possible to provide the intended control with much increasedaccuracy. In this embodiment also, during large-current driving, thesignal generator 13 and constant current circuit 14 permit the gatecurrent to increase within the mirror period whereby the gatedrivability is enhanced. Thus it is possible to speed up di/dt anddv/dt.

Embodiment 5

A power semiconductor device driver circuit in accordance with anotherfurther embodiment is shown in FIG. 12 in block diagram form. Like partsare indicated by like reference numerals as used in FIG. 8 of Embodiment3. In this embodiment the current detection unit is designed to use ashunt resistor 17. A voltage value of shunt resistor 17 is fed back to acentral processing unit (CPU) 71. This CPU 71 permits feedback of thevalue of a main-circuit current to the signal generator 13. Inresponding to receipt of a command voltage from signal generator 13, itprovides constant current control. In this embodiment also, duringlarge-current driving, the signal generator 13 and constant currentcircuit 14 cause the gate current to increase within the mirror periodwhereby the gate drivability is improved so that it is possible to speedup di/dt and dv/dt.

Embodiment 6

A power semiconductor device driving circuit also embodying thisinvention is depicted in FIG. 13 in block diagram form. Like parts areindicated by like reference numerals as used in FIG. 1 of Embodiment 1.Its difference from Embodiment 1 is that the voltage drive type powersemiconductor switching devices to be driven are not the IGBTs 31 and 33but SiC junction FETs 81. The target devices to be driven here may beany available voltage-driven switching devices of the type having mirrorvoltage generation capabilities, including but not limited to Si, SiCand GaN-based semiconductor circuit elements. Additionally, not onlyIGBTs and MOSFETs but also junction FETs are voltage-driven switchingdevices with mirror voltage generatability, and this embodiment is alsoapplicable thereto.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. The gate driver circuit for use with a voltage drive type powersemiconductor switching device, comprising: a drive circuit for giving adrive signal to a gate electrode of the power semiconductor switchingdevice; means for measuring a flow current of the power semiconductorswitching device; and means for switching a gate resistor in the drivecircuit for causing a voltage of the gate to be varied based on adetection value of the flow current of said power semiconductorswitching device such that gate resistance of the power semiconductorswitching device will decrease as gate current of the powersemiconductor switching device increases, further comprising: a constantcurrent circuit in a gate circuit of said power semiconductor switchingdevice; and means for varying a gate current based on a detected valueof the flow current of said power semiconductor switching device.
 2. Thegate driver circuit according to claim 1, wherein an output current ofsaid constant current circuit is changed in a plurality of steps tothereby drive said power semiconductor switching device.
 3. The gatedriver circuit according to claim 1, wherein said constant currentcircuit includes an operational amplifier, a resistor, and a metal oxidesemiconductor field effect transistor (“MOSFET”).
 4. The gate drivercircuit according to claim 1, wherein said means for detecting a flowcurrent of said power semiconductor switching device is a currenttransformer.
 5. The gate driver circuit according to claim 1, whereinsaid means for detecting a flow current of said power semiconductorswitching device is a shunt resistor.
 6. The gate driver circuitaccording to claim 1, wherein said gate driver circuit is a drivecircuit for a silicon carbide (“SiC”) power semiconductor switchingdevice.
 7. The gate driver circuit for a voltage-driven powersemiconductor switching device, comprising: a drive circuit for giving adrive signal to a gate electrode of the power semiconductor switchingdevice; means for measuring a flow current of the power semiconductorswitching device; means for detecting a gate voltage; and means forswitching a gate resistor in the drive circuit for causing a voltage ofthe gate to be varied based on a detection value of the flow current ofsaid power semiconductor switching device and a detected value of thegate voltage such that gate resistance of the power semiconductorswitching device will decrease as gate current of the powersemiconductor switching device increases, further comprising: a constantcurrent circuit in a gate circuit of said power semiconductor switchingdevice; and means for varying a gate current based on a detected valueof the flow current of said power semiconductor switching device and adetected value of the gate voltage.
 8. The gate driver circuit accordingto claim 7, wherein an output current of said constant current circuitis changed in a plurality of steps to thereby drive said powersemiconductor switching device.
 9. The gate driver circuit according toclaim 7, wherein said constant current circuit includes an operationalamplifier, a resistor and an MOSFET.
 10. The gate driver circuitaccording to claim 7, wherein said means for detecting a flow current ofsaid power semiconductor switching device is a current transformer. 11.The gate driver circuit according to claim 7, wherein said means fordetecting a flow current of said power semiconductor switching device isa shunt resistor.
 12. The gate driver circuit according to claim 7,wherein said gate driver circuit is a drive circuit of an SiC powersemiconductor switching device.